1. Field of the Invention
The invention relates to a method for manufacturing the shaft unit of a golf club, more particularly to a manufacturing method which can produce a high quality shaft unit with a long-fiber composite material coated thereon.
2. Description of the Related Art
Referring to FIGS. 1, 2, and 3, a method for manufacturing the shaft unit of a conventional golf club includes the steps of:
(1) providing a shaft 1 which is made of metal and which has a cross-sectional area that increases gradually from an end surface to the other end surface, as shown in FIG. 1;
(2) providing an elongated first-layer sheet 10 which is made of resin and which has several fibers that are coated on the sheet 10 and that are oriented at an angle of about 45 degrees with respect to the sides of the sheet 10, as shown in FIG. 1;
(3) winding the sheet 10 on the shaft 1 in a clockwise direction in such a manner that one of the sides of the sheet 10 is parallel to the axis of the shaft 1 so that the fibers of the sheet 10 form an angle of about 45 degrees with respect to the axis of the shaft 1, as shown in FIGS. 2 and 3;
(4) providing an elongated second-layer sheet 10' which is similar to the sheet 10, the fibers being coated on the sheet 10' and being oriented at an angle of about 90 degrees with respect to the fibers of the sheet 10, as shown in FIG. 1;
(5) winding the sheet 10' on the shaft 1 in a counterclockwise direction in the same manner as the sheet 10 so that the fibers of the sheet 10' form an angle of about -45 degrees with respect to the axis of the shaft 1, as shown in FIGS. 2 and 3;
(6) providing an elongated third-layer sheet 10" which is made of resin and which has several fibers coated on the sheet 10" and that extend along the length of the sheet 10", as shown in FIG. 1;
(7) winding the sheet 10" on the shaft 1 in the same manner as the sheet 10; and
(8) pressurizing and heating the assembly of the shaft 1 and the sheets 10, 10', 10" so as to form the shaft unit of the golf club.
The above described conventional manufacturing process has several drawbacks. Referring to FIG. 4, 4, because the assembly of the sheets 10, 10', 10" is in the form of a spiral, the conventional golf club which is made by the above manufacturing method has a seam 11 formed between the sheets 10 and 10' and a seam 12 formed between the sheet 10' and 10" so that cracks easily occur in the seams 11 and 12. Accordingly, when the golf club is used, the sheets 10, 10', 10" may separate from each other at the seams 11, 12 due to an impact on the sheets 10, 10', 10". This results in decreased strength of the golf club.